Thermodynamic modeling of creep damage in materials with different properties in tension and compression

A constitutive model is developed to describe the creep response of polycrystalline metals and alloys with di€erent behavior in tension and compression. A second-order damage tensor is introduced in order to describe the creep damage under nonproportional loading in nonisothermal processes. The thermodynamic formulation of the creep equation and the damage evolution equation is used to study the creep behavior and creep damage in the initially isotropic materials. The determination of the material parameters in the proposed equations is demonstrated from a series of basic experiments outlined in this paper. The results generated from the model are compared with those obtained from experiments under uniaxial nonproportional and multiaxial nonproportional loading for both isothermal and nonisothermal processes.